The present invention relates to a fifth wheel which is provided on a tractor and adapted to be connected to a king pin fixed to a trailer.
Such a mechanism for connecting a king pin to a fifth wheel has been known as having two locks adapted to be swung to the left and right around lock pins to lock and release the king pin. This known mechanism is, however, faced with a problem in that the inner surfaces of the locks contactable with the king pin are quickly worn down due to repeated start and stop of the tractor, resulting in decrease in comfort of the tractor driver.
Another known mechanism includes a C-shaped lock adapted to be rotated around a lock pin to retain the king pin by a wedging action. In this mechanism, a part of the periphery of the king pin is always kept open leaving a considerable amount of play. This mechanism, therefore, is not satisfactory as a mechanism for connecting the king pin to the fifth wheel. In addition, if the king pin is located at a higher position than the lock, the latter locks only the lower part of the king pin, resulting in an imperfect connection. If the tractor starts in this condition, the king pin may be dangerously disengaged from the lock possibly causing a serious accident such as the trailer falling off.
The specification of British Pat. No. 1407084 proposes an improved mechanism intended for overcoming the above-described problems of the prior art. This mechanism is constituted by a coupling member, slot, coupling hook, latch, operating bar, spring means, connecting bar and other members. In this mechanism, however, the coupling hook and the latch, which make sliding contact with each other, are worn down rapidly the shortening of the life of the latch and hook. In addition, as will be understood from FIG. 1 attached to the specification of the above-mentioned British Patent, the hook does not engage the whole peripheral surface of the pin rather the left upper part of the pin is left open. This arragement causes considerable play, resulting in decreased driver comfort. In addition, the pin is engaged solely by the curved jaw portion of the hook and there is no other member taking part in the locking of the pin. This construction cannot be considered perfect from the view point of safety.